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Kinetic studies on the oxidation of nitrite by horseradish peroxidase and lactoperoxidase

100%
Gębicka L.
Acta Biochimica Polonica
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1999
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vol. 46
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issue 4
919-927
EN
The reaction of nitrite (NO-_2) with horseradish peroxidase and lactoperoxidase was studied. Sequential mixing sopped-flow measeruments gave the following values for the rate constants of the reaction of nitrite with compounds II (oxoferryl heme intermediates) of horseradish peroxidase and lactoperoxidase at pH 7.0, 13.3 ± 0.07 mol^{-1}dm^3s^{-1} and 3.5 ± 0.05 · 10^4mol^{-1}dm^3s^{-1}, respectively. Nitrite, at neutral pH, influenced measurements of activity of lactoperoxidase with typical substrates like 2,2'-azino-bis[ethyl-benzothiazoline-(6)-sulphonic acid] (ABTS), guaiacol or thiocyanate (SCN-). The rate of ABTS and guaiacol oxidation increased linearly with nitrite concentration up to 2.5-5 mmol dm^{-3}. On the other hand, two-electron SCN- oxidation was inhibited in the presence od nitrite. Thus, nitrite competed with the investigated substrates of lactoperoxidase. The intermediate, most probably nitrogen dioxide (*NO_2), reacted more rapidly with ABTS or guaiacol than did lactoperoxidase compound II. It did not, however, effectively oxidize SCN- to OSCN-. NO-_2 did not influence the activity measurements of horseradish peroxidase by ABTS or guaiacol method.
2
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pH Profile of cytochrome c-catalyzed tyrosine nitration

88%
Kambayashi Y., Hitomi Y., Kodama N., Kubo M., Okuda J., Takemoto K., Shibamori M., Takigawa T., Ogino K.
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2006
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vol. 53
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issue 3
577-584
EN
In the present study, we investigated how cytochrome c catalyzed the nitration of tyrosine at various pHs. The cytochrome c-catalyzed nitration of tyrosine occurred in proportion to the concentration of hydrogen peroxide, nitrite or cytochrome c. Thecytochromec-catalyzed nitration of tyrosine was inhibited by catalase, sodium azide, cystein, and uric acid. These results show that the cytochrome c-catalyzednitrotyrosine formation was due to peroxidase activity. The rate constant between cytochrome c and hydrogen peroxide within the pH range of 3 - 8 was the largest at pH 6 (37°C). The amount of nitrotyrosine formed was the greatest at pH 5. At pH 3, onlycytochromec-independent nitration of tyrosine occurred in the presence of nitrite. At this pH, the UV as well as visible spectrum of cytochrome c was changed by nitrite, even in the presence of hydrogen peroxide, probably via the formation of a heme iron - nitric oxide complex. Due to this change, the peroxidase activity of cytochrome c was lost.
3
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The acid-catalyzed interaction of melanin with nitrite ions. An EPR investigation

75%
Matuszak Z., Chignell C. F., Reszka K. J.
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issue 3
475-481
EN
The interaction of synthetic dihydroxyphenylalanine (DOPA) melanin (DM) with nitrite ions, NO2−, in the pH 3.6–7.0 range, has been investigated using electron paramagnetic resonance (EPR). We found that especially at pH <5.5 (from ca. 5.5 to 3.6) the reaction of DM with nitrite generated large quantities of new melanin radicals, which implies the involvement of nitrous acid, HNO2, in the radical formation process. Measurements carried out at constant pH of 3.6 showed that the melanin signal increased together with nitrite concentration, reaching a plateau level which was more than fourfold larger compared to the initial signal amplitude observed in a nitrite-free buffer of the same pH. The effects of nitrite and DM concentrations on the melanin-free radical content were also investigated. It is proposed that the radicals are generated by one electron oxidation of melanin ortho-hydroquinone groups to ortho-semiquinones by HNO2 or related nitrogen oxides such as NO2• radicals. The possible involvement of nitric oxide (•NO) and peroxynitrite (ONOO−) in DM oxidation was also examined. In air-free solutions, nitric oxide per se did not generate melanin radicals; however, in the presence of oxygen a marked increase in the melanin EPR signal intensity was observed. This result is interpreted in terms of the generation of radicals via the oxidation of DM by peroxynitrite. Our findings suggest that melanin can function as a natural scavenger of nitrous acid and some nitrous acid-derived species. This property may be relevant to physiological functions of melanin pigments in vivo.
4
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The efficiency of some fungi species in wastewater treatment

75%
Kadhim N. F., Mohammed W. J., Al Hussaini I. M., Al-Saily H. M. N., Ali R. N., Kadhim N. F., Mohammed W. J., Al Hussaini I. M., Al-Saily H. M. N., Ali R. N.
Journal of Water and Land Development
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2021
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issue 50
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